KDC Settings Configuration settings for the Kerberos Key Distribution Center. KDC Use forest search order This policy setting defines the list of trusting forests that the Key Distribution Center (KDC) searches when attempting to resolve two-part service principal names (SPNs). If you enable this policy setting, the KDC will search the forests in this list if it is unable to resolve a two-part SPN in the local forest. The forest search is performed by using a global catalog or name suffix hints. If a match is found, the KDC will return a referral ticket to the client for the appropriate domain. If you disable or do not configure this policy setting, the KDC will not search the listed forests to resolve the SPN. If the KDC is unable to resolve the SPN because the name is not found, NTLM authentication might be used. To ensure consistent behavior, this policy setting must be supported and set identically on all domain controllers in the domain. Provide information about previous logons to client computers This policy setting controls whether the domain controller provides information about previous logons to client computers. If you enable this policy setting, the domain controller provides the information message about previous logons. For Windows Logon to leverage this feature, the "Display information about previous logons during user logon" policy setting located in the Windows Logon Options node under Windows Components also needs to be enabled. If you disable or do not configure this policy setting, the domain controller does not provide information about previous logons unless the "Display information about previous logons during user logon" policy setting is enabled. Note: Information about previous logons is provided only if the domain functional level is Windows Server 2008. In domains with a domain functional level of Windows Server 2003, Windows 2000 native, or Windows 2000 mixed, domain controllers cannot provide information about previous logons, and enabling this policy setting does not affect anything. KDC support for claims, compound authentication and Kerberos armoring This policy setting allows you to configure a domain controller to support claims and compound authentication for Dynamic Access Control and Kerberos armoring using Kerberos authentication. If you enable this policy setting, client computers that support claims and compound authentication for Dynamic Access Control and are Kerberos armor-aware will use this feature for Kerberos authentication messages. This policy should be applied to all domain controllers to ensure consistent application of this policy in the domain. If you disable or do not configure this policy setting, the domain controller does not support claims, compound authentication or armoring. If you configure the "Not supported" option, the domain controller does not support claims, compound authentication or armoring which is the default behavior for domain controllers running Windows Server 2008 R2 or earlier operating systems. Note: For the following options of this KDC policy to be effective, the Kerberos Group Policy "Kerberos client support for claims, compound authentication and Kerberos armoring" must be enabled on supported systems. If the Kerberos policy setting is not enabled, Kerberos authentication messages will not use these features. If you configure "Supported", the domain controller supports claims, compound authentication and Kerberos armoring. The domain controller advertises to Kerberos client computers that the domain is capable of claims and compound authentication for Dynamic Access Control and Kerberos armoring. Domain functional level requirements For the options "Always provide claims" and "Fail unarmored authentication requests", when the domain functional level is set to Windows Server 2008 R2 or earlier then domain controllers behave as if the "Supported" option is selected. When the domain functional level is set to Windows Server 2012 then the domain controller advertises to Kerberos client computers that the domain is capable of claims and compound authentication for Dynamic Access Control and Kerberos armoring, and: - If you set the "Always provide claims" option, always returns claims for accounts and supports the RFC behavior for advertising the flexible authentication secure tunneling (FAST). - If you set the "Fail unarmored authentication requests" option, rejects unarmored Kerberos messages. Warning: When "Fail unarmored authentication requests" is set, then client computers which do not support Kerberos armoring will fail to authenticate to the domain controller. To ensure this feature is effective, deploy enough domain controllers that support claims and compound authentication for Dynamic Access Control and are Kerberos armor-aware to handle the authentication requests. Insufficient number of domain controllers that support this policy result in authentication failures whenever Dynamic Access Control or Kerberos armoring is required (that is, the "Supported" option is enabled). Impact on domain controller performance when this policy setting is enabled: - Secure Kerberos domain capability discovery is required resulting in additional message exchanges. - Claims and compound authentication for Dynamic Access Control increases the size and complexity of the data in the message which results in more processing time and greater Kerberos service ticket size. - Kerberos armoring fully encrypts Kerberos messages and signs Kerberos errors which results in increased processing time, but does not change the service ticket size. Not supported Supported Always provide claims Fail unarmored authentication requests Warning for large Kerberos tickets This policy setting allows you to configure at what size Kerberos tickets will trigger the warning event issued during Kerberos authentication. The ticket size warnings are logged in the System log. If you enable this policy setting, you can set the threshold limit for Kerberos ticket which trigger the warning events. If set too high, then authentication failures might be occurring even though warning events are not being logged. If set too low, then there will be too many ticket warnings in the log to be useful for analysis. This value should be set to the same value as the Kerberos policy "Set maximum Kerberos SSPI context token buffer size" or the smallest MaxTokenSize used in your environment if you are not configuring using Group Policy. If you disable or do not configure this policy setting, the threshold value defaults to 12,000 bytes, which is the default Kerberos MaxTokenSize for Windows 7, Windows Server 2008 R2 and prior versions. Request compound authentication This policy setting allows you to configure a domain controller to request compound authentication. Note: For a domain controller to request compound authentication, the policy "KDC support for claims, compound authentication, and Kerberos armoring" must be configured and enabled. If you enable this policy setting, domain controllers will request compound authentication. The returned service ticket will contain compound authentication only when the account is explicitly configured. This policy should be applied to all domain controllers to ensure consistent application of this policy in the domain. If you disable or do not configure this policy setting, domain controllers will return service tickets that contain compound authentication any time the client sends a compound authentication request regardless of the account configuration. Mode: Forests to Search Syntax: Enter the list of forests to be searched when this policy is enabled. Use the Fully Qualified Domain Name (FQDN) naming format. Separate multiple search entries with a semi-colon ";". Details: The current forest need not be listed because Forest Search Order uses the global catalog first then searches in the order listed. You do not need to separately list all the domains in the forest. If a trusting forest is listed, all the domains in that forest will be searched. For best performance, list the forests in probability of success order. Claims, compound authentication for Dynamic Access Control and Kerberos armoring options: Ticket Size Threshold